The principle of valve lift switchover in internal combustion engines is known in the prior art. Thus, for example, systems such as Porsche's Vario Cam Plus have already been in series production for some years (see also “Handbuch Verbrennungsmotor” (“Combustion engine manual”), editor: van Basshuysen/Schäfer, published by Vierweg Verlag, 1st edition, April 2002). A continuing problem with this technology continues to be the valve lift switchover process as such. Switching from a small to a large valve lift in particular creates difficulties in respect of the torque neutrality of the internal combustion engine. Absence of torque neutrality of the internal combustion engine expresses itself in a noticeable bucking of the motor vehicle during the switchover from one valve lift to the other. The reason for the lack of torque neutrality lies in scarcely avoidable inaccuracies in the absorption coefficient or volumetric efficiency model (intake manifold model) of the internal combustion engine.
Said models, which run in the engine management system and are supplied therein with the corresponding operating data of the internal combustion engine, calculate the air mass supplied to the combustion process as a function of the operating point. From this, the fuel quantity that is to be injected is calculated with adherence to a specific air/fuel ratio and taking into account the predefined lambda value. Said fuel quantity in turn determines the expected torque of the respective combustion cycle of the internal combustion engine.
A separate model is stored in the engine management system for each valve lift configuration. The model data is stored in characteristic maps which are formed from what are referred to as sampling points. The quality criterion for the switchover is that the actual engine torque in both configurations—i.e. directly before and after the valve lift switchover—is the same as far as possible. However, even small errors in the model calculation lead to differences in torque and consequently to inaccuracies in the valve lift switchover.
A further problem at this juncture is that the combustion-related behavior of the internal combustion engine usually changes as a result of the valve lift switchover. This is mainly to be expected with channel injectors due to the changed flow cross-section at the valve. A further problem arises if, in the course of the valve lift switchover, a change in combustion behavior takes place, for example when a spark-ignition combustion process transitions to a controlled self-ignition.
In principle the models running in the engine management system can be executed with any desired degree of precision. However, the problem here is that the complexity of the models increases rapidly if all the parameters influencing a quantity to be mapped are to be recorded with a particular precision. Even modern engine management systems quickly reach their limits at this point. In this case the memory storage capacity and computing capacity of the engine management system are rapidly exhausted, with the result that ultimately compromises and sacrifices have to be made with regard to precision.